Oxidation and volatilization of TZM alloy in air

• Published in: Journal of nuclear materials 2000-12, Vol.283, p.1458-1462
• Main Authors: Smolik, G.R., Petti, D.A., Schuetz, S.T.
• Format: Article
• Language: English
• Subjects: 07 - ISOTOPES AND RADIATION SOURCES, 36 - MATERIALS SCIENCE, 70 - PLASMA PHYSICS AND FUSION TECHNOLOGY; ALLOYS; chemical reactivity; EVAPORATION; FLOW RATE; fusion reactor safety; GASES; MASS TRANSFER; mass transport; MOLYBDENUM; MOLYBDENUM ALLOYS; OXIDATION; OXIDES; OXYGEN; RADIOACTIVITY; redeposition; REFRACTORY METALS; SAFETY; SATURATION; THERMAL CONDUCTIVITY; THERMODYNAMICS; THERMONUCLEAR REACTOR MATERIALS; TRANSPORT; TZM alloy; VAPOR PRESSURE; volatilization
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/S0022-3115(00)00303-2

The excellent high temperature strength and thermal conductivity of molybdenum-base alloys provide attractive features for components in advanced magnetic and inertial fusion devices. Refractory metal-base alloys react readily with oxygen and other gases, and molybdenum alloys are susceptible to losses from highly volatile molybdenum trioxide (MoO 3) species. Transport of radioactivity by the volatilization, migration and re-deposition of MoO 3 during a potential accident involving a loss of vacuum or inert environment represents a safety issue. We have experimentally measured the oxidation, volatilization and re-deposition of molybdenum from TZM in flowing air between 400°C and 800°C. Calculations using chemical thermodynamic data for vapor pressures over pure MoO 3 and a vaporization mass transfer model correlate well with the experimental data between 600°C and 800°C. Partial saturation of (MoO 3) gas species accounts for influences of flow rate at 700°C. Some anomalies in oxidation rate below 650°C suggest that other phases, e.g., MoO 2 or other non-stoichiometric oxides may influence oxidation and volatilization processes under some limited conditions.